• To use farmer scale machinery to evaluate the benefits of adopting zone
management farming on a range of soil types over a three year period;
• To increase the output to input ratio for our farming system; and
• To collaborate with, and add value to research in precision agriculture being
undertaken by CSIRO, the Department.of Agriculture and University of Western
Australia (UWA).

Yield stability and Adopting VRT.
In the initial phase of the project, trial paddocks were selected that had a high degree of
variability. The aim was to exploit this variability to increase whole paddock profitability.
As we learnt more about crop performance in individual paddocks, it became apparent
that some paddocks had a high degree of variability from season to season as well as
between zones (i.e. a high performing zone one season could be a low performing zone
the next). This makes using variable rate technology (VRT) to achieve target yields is
very difficult.
We have developed some rules of thumb for determining if VRT is likely to be profitable
based on the percentage of the paddock that is stable through time.
Highly suited to VRT = >70% Stable
May suite VRT = 55-70% Stable
Unlikely to suit VRT = <55% Stable
Our research shows that unstable zones within a paddock are usually impeded by soil
physical or chemical constraints such as water logging, sub soil acidity, sub soil
compaction. Water logged sites tend to be low yielding in wet seasons and high yielding
in dry years. Sites with subsoil problems tend to perform like medium zones in seasons
with a soft finish and like low zones when there is a dry end to the season.
Trial results have given economic responses (up to 500kg/ha) in the first season to deep
ripping to overcome a tight subsoil.
Most trial sites have not given economic yield responses to additional applications of
nitrogen, phosphate (and potassium on some sites). To date the most profitable treatment
has been the low fertiliser input strategy in high or low yielding seasons.
7
Water Storage Determines Yield
University of Western Australia honors student Josh Whitwell joined the project to assess
how water holding capacity of soil affects yield in that zone. Josh found that grain yield
was determined mainly by a soil’s ability to store and supply water to plants. The high
productive zones commonly had soil profiles that could store larger amounts of water and
supply it back to the crop. Of the 45 sites investigated, 40 were found to have limited
rooting depth due to critical amounts of pH, EC and soil strength. This suggests there is
scope to increase grain yield by ameliorating subsoils.
Focus for 2006 and 2007
With the project extension now approved we intend to focus on continuing research on
the main trial sites to increase replication through time. We hope with the additional two
trial years we can better understand how seasonal conditions interact with zone
management.
We also intend to compare the different paddock zoning methods used by our
collaborating partners, Gamma radiometrics, (B Whelan, Sydney University) and Crop
biomass image analysis (I Mailing, Silver Fox) with zoning from actual yield data.
Economic Analysis
Over the three trial years we have seen a large fluctuation in fertiliser cost and grain
prices.
For all economic calculations the prices have been standardized to eliminate year to year
fluctuations in grain price or fertiliser cost. This has enabled comparisons through time.
• Wheat price – A net in bank wheat price of $180/t plus or minus AWB golden
rewards quality bonification (July 2005). The $180 net in bank price reflects the 5
year average for wheat delivered Corrigin.
• Malt and Feed Barley price – A net in bank wheat price of $198/t (malt) and $153/t
(feed) plus or minus quality bonification. The net in bank price reflects the 5 year
average for barley delivered Corrigin.
• Lupin price - $190 net in Bank.
• Canola price - $355/t net in Bank plus and minus oil bonification as per grain pool
July 2005. This reflects the 5 year average net in bank canola price for Corrigin.
• Fertiliser prices – 2004 Company list prices were used for all 3 trial years.

This trial demonstrates that in a dry year like 2002 lupin grain yield can be increased or at
least maintained by increasing lupin row spacings. This increase in yields has resulted
from a combination of increased pod height and additional grain production. Widening
row spacing on lupins also allows for machinery to better handle residue from previous
crops.
Although lupins sown at 460mm spacings had equivalent yields to those lupins sown on
920mm spacings, there is a feeling that the 920mm sowings would not perform as well in
a higher lupin yielding season. Also lupins sown on 920mm spacings produced less
biomass, which would result in less nitrogen being fixed for the following cereal crop.

Deep ripping 2002
The deep ripped plots grew more biomass (Figure 2) and yielded 28% more than the
control plots (2.15 t/ha compared to 1.68 t/ha) see figure 3. This resulted in an increased
return of $85/ha. After the cost of ripping has been deducted an additional $47/ha of
income was generated by deep ripping (Economics use a net in bank price of $180/t plus
AWB bonification).
The ripping response is likely to be from a combination of:
• improved water use;
• access to accumulated nutrients deeper in the soil profile; and
• mineralisation of nitrogen due to the cultivation effect.
There was little difference in grain quality between ripped and un-ripped control plots.

Potash application
Applying 70kg/ha of Murate of Potash (MOP) was adequate to alleviate the potassium
deficiency. Increasing MOP rates to 120kg/ha did not economically increase grain yield.

Optimize crop nutrition across productivity zone 

In a very low rainfall season reducing fertiliser inputs can be the most economical
strategy. Across all productivity zones, the low fertiliser treatment was the most
profitable treatment. Delaying nitrogen and potassium applications allows more strategic
use of inputs.
The 2002 season did not provide adequate rainfall for crop yields to achieve the medium
and high target yields. The high productivity zone was the highest yielding zone in the
trial.

Responsiveness of Wheat to nitrogen.

The high productivity zones within the paddock gave a larger grain yield in response to
increasing fertiliser inputs. However in this dry season the yield responses were not
sufficient to cover the additional input costs. Reducing seed and fertiliser rates on poor
performing deep sands can maintain grain yield and increase gross return by $167/ha in a
dry season.

In a very low rainfall season reducing fertiliser inputs can be the most economical
strategy. Delaying nitrogen applications in dry seasons allows more strategic use of
inputs. The use of variable rate technology is unlikely to be profitable in a decile 1
season.

The yields of the canola were severely limited by drought (260-380kg/ha). April to
October rainfall was 160mm, making 2002 a decile 1 season. Because of the failed crop
and expense of harvest only the high and medium productivity zones were harvested.
Productivity zones
Both high and medium productivity zones achieved equivalent yield (0.32t/ha, Table 2),
however, the medium zone achieved an additional two percent oil. The biomass image
indicates that there was a biomass response to the high input treatments (Figure 2).
Nutrient input
The failed crop resulted in negative gross margins for all levels of inputs. The most
economical treatment for all productivity zones in the trial site was the low fertilizer
input. The low fertilizer input treatment had savings of $32 and $104 over the medium
and high input treatments.

Conclusion

In a very low rainfall season reducing fertiliser inputs can be the most economical
strategy. Delaying nitrogen and potassium applications in late break years allows more
strategic use of inputs.

Deep ripping to a depth of 80cm to alleviate a tight subsoil resulted in a 470kg response
in wheat yields in the dry season of 2002. This increased yield netted an additional
$49/ha after paying for the cost of deep ripping. Applying 2t/ha of lime increased grain
yields on the unripped plots but did not increase yield on the deep ripped plots.

Farmers can confidently sow lupins on 50cm row spacings to allow easy stubble handling
at seeding and know that it will not compromise lupin yield or the yield of wheat
following the lupins. In this trial the combined benefit of increased lupin yield ($12) and
wheat yield ($28) returned an extra $40/ha compared to conventional lupin 23cm row
spacings.
Paddocks with a high percentage of instability will be difficult to implement variable rate
technology for applications of fertiliser, because zones within the paddock perform very
differently from season to season.
When paddocks have sound phosphate levels and low PRI levels varying phosphate rates
in the short will have minimal impact on crop performance. Savings made can greatly
increase paddock profitability.

Increasing the productivity of hard setting grey clay by applying 2t gypsum and 1t
of lime then deep ripping to a depth of 50cm.

Crop establishment on the deep ripped site was poorer with only 52 plants/m2 compared
to the unripped with 97 plants/m2. Tissue tests revealed that the site that was deep ripped
had higher levels of all nutrients (including potassium). Although the deep ripped
treatments had less plants per meter established when biomass cuts were done, on a meter
row the deep ripped sites had the greater biomass (ripped 202g and unripped 188g).
When comparing the grain yield of ripped verse control plots there was a large yield
penalty for deep ripping (2.11t/ha ripped and 2.7t/ha control). The deep ripped plot
returned $171/ha less income than the ripped plots.

In the high yielding season of 2003 there was a canola biomass response to deep ripping
(See figure 3). However, it is surprising to find that the increased biomass grown on the
deep ripped plots did not result in increased grain yield (Table 1).
Likely reasons for no yield response to deep ripping in canola:
• It is most likely that the canola achieved its water non-limited yield potential and
factors other than soil rooting depth limited crop yield.
• It is possible that the high aluminium levels in the subsoil prevented the canola
from converting the increased biomass to yield.

Investigate how beneficial deep ripping and applying lime in 2002 is for canola
sown in 2003.

There was a massive biomass response to deep ripping however this did not follow
through to the canola yields. There was a deep ripping by liming interaction where by
ripping without liming lost five percent yield over the control plots and ripping plus
liming out yielded the control plots by five percent. There was an 11% response to the
application of 2t/ha of lime in 2002 on the canola grown in 2003 returning an extra
$43/ha.

An eight percent yield increase was achieved by deep banding lime prior to sowing
barley compared to top dressing lime. The response was not adequate to cover the cost of
deep ripping. Deep ripping was relatively un-responsive, with only a three percent yield
increase. This is not surprising given the high aluminium levels in the sub soil and barley
is sensitive to high aluminium levels. The un-replicated demonstration plot of deep
banding 300kg of sheep manure was the highest yielding treatment in the trial.

Although the crop yield responded to additional fertiliser in the high and medium
productivity zones the extra grain yield did not cover the fertiliser and application costs.
In the low productivity zone (deep white sand) additional nitrogen, phosphorus and
potassium increased grain yield enough to cover the cost of the extra fertiliser. This was
surprising given the low potential of this soil type.

To investigate the soil pathogen levels and to determine if the pathogen levels vary
according to productivity zones in the paddock.

Increasing the nitrogen supply gave a visual biomass response in the NDVI biomass
image.
The grain yield in this paddock was very responsive to increased nitrogen rates in all
productivity zones. In the low and high productivity zone the high nitrogen treatment
gave the highest yield and profit of all treatments. In this paddock it appears unlikely that
applying nitrogen using variable rate technology would be more profitable than treating
the paddock as one unit. On average the paddock would be best managed by applying the
high nitrogen rate across all productivity zones.
The PredictaB tests in all productivity zones showed very low levels of disease except the
low productivity zone where medium levels of Common root rot were measured.

Investigate how beneficial deep ripping and applying lime in 2002 is for wheat
crop sown in 2004.

Over the 3 years of the trial the greatest yield responses have resulted from the
combination of deep ripping and liming. However due to the expense of the treatments
($150/ha) it has not been the most profitable treatment ($73/ha, Table 3).
Deep ripping without liming has generated the greatest return ($78/ha) over the three year
period after paying for the treatment cost ($70/ha). However there was a yield loss in the
canola phase and over time its expected that the deep ripping and lime treatments will
generate the greatest profit.
Applying 2t/ha of lime at a cost of $70/ha has generated a profit of $45/ha after paying
for the cost of lime. This is a very rapid return on a liming investment; usually it takes
four years to generate a profit from liming.

The visual biomass image shows no sign of a response to increased phosphate
applications (See figure 1). This indicates that due to the high background phosphate
levels (26 – 56ppm of phosphate) the lupin crop was not limited by phosphate.
The lupin grain yield in the high productivity zone was unresponsive to additional
phosphate (Table 2). However in the medium productivity zone there was a lupin yield
response to applying additional phosphate. The high fertiliser input treatment returned an
additional $23 over the low and $16/ha over the medium fertiliser input treatments after
paying for the additional fertiliser.
38
Due to communication errors between technical support and farmer, the treatments in the
low productivity zone were not harvested. There is significant variability between plots
so care needs to be taken with interpreting this data.

Conclusion

With high soil phosphate levels lupins can be unresponsive in crop biomass and grain
yield. Economic responses were achieved by applying additional phosphate in the
medium productivity zone, but this was no the case in the high productivity zone.
Care must be taken in drawing strong conclusions from this data due to variability in the
plot yields.

As fertiliser inputs were increased, canola biomass increased. However this did not
follow through to grain yield. There was only a nine percent yield increase achieved by
spending an extra $43 on fertiliser when increasing rates from low to medium levels.
Further increases in fertiliser gave no additional yield. The low productivity site gave the
highest grain yield and the high productivity zone had the lowest grain yield. This was
caused by the dry finish to the season and the different soil properties of each zone.

Deep ripping to overcome subsoil compaction is extremely profitable prior to sowing
wheat even in a dry year like 2002. After the cost of ripping an additional $47/ha was
generated in the first season. In a low yielding season (1.2-1.5t/ha) applying potassium to
soils with 40-50ppm potassium can still give an economical yield response ($42/ha).
When sowing back over the deep ripped sites the following season with canola, there was
an increase in canola biomass there was no additional grain yield.
There was no increase in barley grain yield or crop biomass in 2004 in response to the
deep ripping in 2002. However the barley grown on the ripped plots had significantly
lower screenings than the control plots and was acceptable as malt barley where as the
control plots only made feed grade, this increase in grain quality returned an extra $74/ha.
Over a three year period the net benefit to deep ripping was $121/ha. There could well
have been even grater response to ripping if the paddock had have been limed as well as
deep ripped. This may have alleviated some of the subsoil acidity and Aluminium
toxicity levels and enabled Aluminium sensitive crops like canola and barley to benefit
more from the deep ripping.

Conclusion

The crop biomass was responsive to fertiliser input in all productivity zones, with high
input plots consistently having the highest biomass and the low input plots consistently
the lowest. In the high and medium productivity zones the high input treatment gave the
highest grain yield. This yield increase was only just adequate to cover additional
fertiliser costs in the high productivity zone. In the medium zone the additional yield did
not cover the cost of the extra fertiliser. Averaged across all sites the most profitable
fertiliser treatment was the low input treatment returning $223/ha (Figure 1).
There is a poor correlation between crop biomass and grain yield. For example the low
productivity zone had the highest crop biomass but the lowest grain yield.